Method of inspecting electric lamp filaments



Patented Oct. 23, 1951 METHOD OF INSPECTING ELECTRIC LAMP FILAMENTS Robert B. Reid, Beverly, Mass., assignor to Sylvania Electric Products 1110., Salem, 'Mass a corporation of Massachusetts No Drawing.

1 Claim.

This invention relates to electric lamp fila ments and more particularly t a method of inspecting the same during the manufacture thereof. y

In the process of forming coiled or coiled-coiled electric lamp filaments from tungsten wire, the wire is subjected to several operations, some of which include machine operations, such as primary coiling and secondary coiling, for example. When the wire is subjected to a machine op ration, there is always the possibility that it may become contaminated with oil since the machinery is usually quite delicate and must always be properly lubricated. The presence of even a small amount of oil on the tungsten wire is harmful because, when the wire is heated, either during processing or by passing current therethrough in the finished lamp, the wire becomes more brittle than wire which has not been so contaminated, and some of the electrical characteristics of the finished lamp differ from those of lamps whose filaments have been so contaminated. The abnormal brittleness and erratic electrical characteristics are probably due to the formation of tungsten carbide when the oil-contaminated tungsten wire is heated to a temperature sufficient to break down the oil, such as during actual lamp operation, for example.

The inspection method of my invention materially reduces the possibility of oil-contaminated filaments being used in making electric lamps. This method comprises subjecting the tungsten wire, during at least one stage in the process of its fabrication into an electric lamp filament, to inspection under a source of ultraviolet light. Since most petroleum oils normally fiuoresce when exposed to an ultra-violet light source, unless they have been treated to remove this characteristic, and since petroleum oils are usually employed as machine lubricants, the tungsten wire, if it has been contaminated by the machine lubricating oil, will fiuoresce. An inspecting operator can then remove the fluorescing wire.

However, there are certain oils which may be used in connection with electric lamp manufacture and filament forming processes which do not fiuoresce.

For example, certain machine parts, such as the metal pin on which the secondary coil of a coiled-coiled filament i wound, are usually kept immersed in a mineral oil when not in use. Unless this oil is completely removed from those parts or portions thereof which may come in contact with the tungsten wire, contamination Application March 31, 1949, Serial No. 84,737 7 will result. Since mineral oil does not normally fluoresce, it may be caused to do so by the addition thereto of a fluorescent dye which is soluble therein or by the addition of a fluorescent petroleum oil which is soluble therein. The quantity of dye or oil added to the mineral oil does not have to be very great to effect the desired result. Although the exact quantity thereof is not critical, enough must be added to impart fluorescence. When this is done, coils r wire which have been contaminated by a normally non-fluorescing mineral oil can be detected by an inspector and the situation remedied. For example, I have used an American mineral oil having a specific gravity of about 900 and a viscosity of about 350 centipoises and imparted fluorescence thereto by adding a soluble, fluorescing, petroleum, machine-lubricating oil.

The fabrication of an electric lamp filament from tungsten wire usually comprises winding the wire on a molybdenum or steel mandrel to form the primary coil, annealing to effect a setting of the wire and the mandrel, coiling the primary coil, if a coiled-coiled filament is to be made, to form the secondary coil, sintering t effect a setting of the secondary coil, and finally immersing in an acid bath to remove the mandrel, leaving the finished coil.

Since the primary and secondary coiling operations are machine operations, it is most desirable that inspection take place during or after these steps in the fabricating process. Since it is always possible for the tungsten wire as received from a supplier to be contaminated with oil, an initial inspection may be advantageous before the filament forming process is started. After the tungsten wire has been fabricated into an electric lamp coil and before it has been sealed within a lamp envelope, there is a possibility that it might become oil-contaminated, at the lamp sealing-in machine, for example. In order to check on this source of oil-contamination, a fluorescent dye, such as cinchonine, for example, may be added to the butyl-phthalate trap usually employed on lamp sealing-in machines. These traps are usually disposed in the vacuum line to prevent a leaky lamp or a leaky machine head from destroying the vacuum in the entire line by the admission therein, through the leaky lamp or leaky head, of air, etc., from the room atmosphere at the machine.

Since different oils may be used on the machines or parts thereof employed in the fabrication of a lamp filament from tungsten wire, and since the color which characterizes the fluorescence of one oil may not be readily distinguishable from the color which characterizes the fluorescence of another oil, the practical value of my inspection method may be enhanced considerably by introducing into each oil used a diiTerent fluorescent oil-soluble dye s 'thatan inspecting operatorlcarr'readilydetermine, from the color of fluorescence, the source of the contaminating oil. This determination of the source of con-- tamination renders the tasl; of effecting remedial action quite simple.

What I claim is:

The method of determining: thesource of contaminating oil on tungsten wire during thefabrication of electric lamp filaments therefrom.

which comprises adding a different colored .oilsoluble fluorescent dye to each of a plurality'of oil-bearing parts of the machine on which" the filaments are fabricated, and inspecting saidwire.

under a source of ultraviolet light during the 20 4 fabricating process to detect the presence of contaminating oil thereon.

ROBERT B. REID.

REFERENCES CITED The following references? are of? record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,142,865 Zabel Jan. 3, 1939 2,359,114 Jebens-et a1 Sept. 26, 1944 2,434,458 Wade Jan. 13, 1948 OTHER REFERENCES Luminescence, Pringsheim et al., published by Interscience Publishers, Inc. (1943), New York, Nl Yz pages 118-124. 

